This document provides an overview of the 7-layer OSI model. It describes each layer from the physical layer to the application layer, including their key functions. The physical layer deals with physical equipment for data transmission like cables and switches. The data link layer forms frames from packets and performs error detection. The network layer delivers packets through logical addressing and routing. The transport layer provides reliable data delivery through segmentation, error control, and flow control. Higher layers include the session layer for managing communication sessions, the presentation layer for data translation and encryption, and the application layer for end-user software interaction.

1. OSI MODEL
SUBJECT: NETWORKING
COURSE : DIPLOMA IN INFORMATION
TECHNOLOGY (DIT)
INSTITUTE : SHAHEEN VOCATIONAL
TRAINING INSTITUTE (SVTI) NAWABSHAH

2. 2

3. 3
• This layer includes the physical equipment
involved in the data transfer, such as the
cables and switches.
• This is also the layer where the data gets
converted into a bit stream, which is a string
of 1s and 0s
• The main functionality of the physical layer is
to transmit the individual bits from one node
to another node
PHYSICAL LAYER (LAYER 1)

4. • The second layer of OSI model is data link
layer.
• It is responsible of node to node data delivery.
• It forms frame from the packets that are
received from network layer
4
Data link layer
(layer 2)

5. FUNCTIONS OF DATA LINK LAYER
• The data packets received from
the network layer are
encapsulated in frames by data
link layer
• During data transmission, due to
signal loss, error might occur in
the data being transmitted.
• To minimize such data error, the
data-link performs error
detection and correction
techniques on the transmitted
data.
5
FRAMING ERROR DETECTION
MEDIA ACCESS CONTROL
• In the network when multiple
devices share the same
communication channel , this
leads to data collision in the
network channel.
• To prevent such collision, the
datalink layer performs checks on
the devices with the same
network channel to avoid
collision.

6. NETWORK LAYER (LAYER 3
6
• The third layer of OSI model is network layer.
• The main responsibility of network layer is delivery of
data packets from the source to destination.

7. FUNCTIONS OF NETWORK LINK LAYER
• Logical addressing is to
distinguish between source
and destination.
• In a network, there are
multiple routes available
from source to destination .
• The network layer decides
efficient or shortest path to
be taken
7
Logical addressing Path determination
Routing
• The network layer is
responsible for receiving
frames from the data link
layer, and delivering them to
their intended destinations
among based on the
addresses contained inside
the frame.

8. TRANSPORT LAYER (LAYER 4)
9
• The transport layer (layer 4) is responsible for delivery of
an entire data from an application program on the source
device to a similar application program on the destination
device.
• Provides transfer of data between end users, providing
reliable data delivery.

9. FUNCTIONS OF
TRANSPORT LAYER
9
Segmentation
One message is splitted into different segments, and
every segment has own sequence number.
All messages are reassembled accurately upon reach at
the their target destination.

10. 9
Error control
•The data link layer checks for the error between each
network. If an error is introduced inside one of the
routers, then this error will not be caught by the data
link layer.
•It only detects those errors that have been
introduced between the beginning and end of the link.
•Therefore, the transport layer performs the checking
for the errors end-to-end to ensure that the packet
has arrived correctly.
FUNCTIONS OF
TRANSPORT LAYER

11. 9
Flow control
• Flow control is used to prevent the sender from
overwhelming the receiver. If the receiver is
overloaded with too much data, then the receiver
discards the packets and asking for the
retransmission of packets.
• This increases network congestion and thus,
reducing the system performance. The transport
layer is responsible for flow control.
FUNCTIONS OF
TRANSPORT LAYER

12. SESSION LAYER (LAYER 5)
9
• The session layer creates communication channels, called
sessions, between devices.
• It is responsible for opening sessions, ensuring they remain
open and functional while data is being transferred, and
closing them when communication ends.

13. Session management
9
• Provides the mechanism for opening, closing and managing a
session between end-user application processes, i.e., a semi-
permanent dialogue.
• Communication sessions consist of requests and responses that
occur between applications.
Functions of Session layer

14. Authentication
9
• Before establishing a session with some network peer, it
is important for one of the computers to know that
another peer it is communicating to is a legitimate one.
• In short terms, you can say that authentication is the
process of verifying that "you are who you say you are".
Functions of Session layer

15. Authorization
9
• Authorization is the process of verifying that "you are
permitted to do what you are trying to do“
• After authentication user will authorize to access
information.
Functions of Session layer

16. Presentation layer (layer 2)
9
• The presentation layer prepares data for the application
layer. It defines how two devices should encode, encrypt,
and compress data so it is received correctly on the other
end.

17. FUNCTIONS OF PRESENTATION LAYER
9
Translation
• The data that the presentation layer receives from the
application layer is a series of characters and numbers,
the data must be converted to bit streams to be readable
by the receiving computer.

18. 9
Encryption and Decryption
• Encryption is the process of scrambling data so that it's
unreadable to unauthorized parties, and decryption is the
process of converting the scrambled data back to a readable
form.
• Because computer systems often handle sensitive information,
the presentation layer performs both of these important
security tasks.
FUNCTIONS OF PRESENTATION LAYER

19. 9
Data compression
• Compression is the process of reducing data size. This process
is helpful for transmitting data because smaller files transmit
more quickly.
• The presentation layer performs compression on the sender's
side to reduce the bandwidth of the transmitting data and
accelerate its rate of transmission.
FUNCTIONS OF PRESENTATION LAYER

20. APPLICATION LAYER (LAYER 1)
9
• The application layer is used by end-user software such as
web browsers and email clients.
• The application layer in the OSI model is the closest layer to
the end user which means that the application layer and end
user can interact directly with the software applicationdata to
users

21. Study Material for
Reference
HTTPS://REALPARS.COM/OSI/
HTTPS://WWW.LIFEWIRE.COM/LAYERS-OF-THE-OSI-
MODEL-ILLUSTRATED-818017
HTTPS://YOUTU.BE/VV4Y_UONEC0